572 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



The longest remaining portion of the more or less broken arms is 10 mm. long, 

 with a thickness of 0.5 mm. at the base, and of 0.33 mm. at the end, from which 

 it may be inferred that the missing portion had at least the same length. This 

 arm stump, composed of 20 brachials, bears 9 pinnules on one side and 10 pinnules 

 on the other. 



At the time of detachment from the larval column the arms of Antedon bifida 

 bear only five pinnules, three on one side and two on the other, and Pj is the only 

 pinnule developed in the proximal portion. 



The brachials have the same form as in the adults, but they are proportionately 

 longer. 



In Antedon bifida at the time of detachment the articulations between the 

 brachials have not as yet become oblique. 



Syzygies are present between brachials 3+4, 9+10, 14+15, 18+19, and 

 22+23, just as in the adult. Many of the arms are broken at the first syzygy, and 

 the radial striation of the distal articular face of the third brachial can be easily 

 seen. 



The three or four lowest pairs of pinnules are very slender and hairlike. 

 P x is very long, composed of from 12 to 14 segments (in the adults of from 25 

 to 35), without tentacles, and with a few very small scattered sacculi, which, 

 though sometimes arranged in pairs very close to each other, form, however, only 

 a single row. 



The two or three following pinnules are scarcely half as long as P 15 which in 

 the fully grown animal is often fully three times as long as they are. 



Professor Sars finds that in the fully grown Hathrometra sarsii, more or less 

 adult, the two pinnules on either side of the arm which immediately follow P 1 are 

 similarly very slender, almost hairlike, without tentacles, and in certain cases 

 even without gonads, which, like the tentacles, are not present before the fourth 

 pair of pinnules. 



P 5 in the same individual has about the same length as the pinnule immedi- 

 ately preceding, but, like the following, it has the usual form, thick at the base 

 and gradually tapering toward the tip. It is composed of 9 segments, and, like 

 all those following, it is provided with tentacles and with sacculi, there being 

 6 pairs of the latter in two alternating rows. P 6 has 13 pairs of sacculi. Ordi- 

 narily there are on the arms 1 or 2 pairs, and on the pinnules 2 or 3 pairs of 

 sacculi to each segment. 



The following pinnules become gradually somewhat longer. 

 At the end of this stage the perfectly developed pentacrinoid is ready to 

 detach itself from its column and to lead a free existence. All the essential struc- 

 tures of the free adults are present, although many of them are not so numerous 

 as they will become later. 



Professor Sars notes that there is, however, reason for believing that at the 

 time of discarding the larval column the pentacrinoids are not always so perfectly 

 developed as the specimen from Manger just described; for from March to June 

 there were dredged among the Lofoten Islands (at the Guldbrand Islands in 100 



